Re: [PATCH 34/35] async: use workqueue for worker pool

From: Frederic Weisbecker
Date: Tue Jun 29 2010 - 11:52:24 EST

On Tue, Jun 29, 2010 at 05:46:32PM +0200, Tejun Heo wrote:
> Hello,
> On 06/29/2010 02:18 PM, Frederic Weisbecker wrote:
> >> Yeah, well, that's kind of the whole point of cmwq. It would try to
> >> minimize the number of used workers but the provided concurrency will
> >> still be enough. No async probe will be stalled due to lack of
> >> execution context and the timings should be about the same between the
> >> original async implemetnation and cmwq based one.
> >
> > Right. I just don't know what is supposed to be slow on boot that
> > needs to use async. Is that because reading some ports is slow or
> > because we need to do something and wait for some times to get the
> > result.
> It's things like ATA bus resetting and probing. They're usually
> composed of short CPU activities and rather long sleeps.


> > If there is a question of slow ports to probe, then cmwq wouldn't seem the
> > right thing here, as it only forks when we go to sleep.
> I lost you here. If something during boot has to burn cpu cycles
> (which it shouldn't, really), it has to burn cpu cycles and having
> multiple concurent threads won't help anything.

It would on SMP.

> If something doesn't
> burn cpu cycles but takes long, it gotta sleep and cmwq will start a
> new thread immediately. So, can you please elaborate why cmwq would
> be problematic?

No in this case it's not problematic, as far as the things that were using
async have a small cpu burn and long sleep waiting, it looks like cmwq
fits :)

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